I have to disagree with the first sentence. I think WAR treats DH's fairly because they only play half the game.
By the same token the highest WAR a closer has ever had is probably around 4.
6 WAR is huge for a DH. Also, 6 WAR on the free agent market costs about 50 million on average, so obviously I don't disagree about prime Papi being worth a ton of coin.